1. Field of the invention
The present invention relates to a method for manufacturing a carbon composite material. More particularly, it relates to a method for manufacturing a carbon composite electrode material used as a negative electrode active material in lithium secondary batteries.
2. Description of the Related Art
It was reported that when a certain type of carbon material, of carbon composite electrode materials, is used as a negative electrode active material in lithium secondary batteries, the charge-discharge cycle characteristic and safety of the secondary batteries is excellent (for example, Japanese Patent Unexamined Publication Nos. Sho 63-24555 and Hei 1-311565). This carbon material is manufactured, for example, by chemical vapor deposition (CVD) of a hydrocarbon.
The inventors of this application found out and disclosed the fact that outstandingly excellent as the negative electrode active material in lithium secondary batteries was particularly a carbon material of a structure such that its internal layer had high crystallinity and that its surface layer was coated with a carbon having a turbulent layer structure (Japanese Patent Application No. Hei 3-144547).
As manufacturing methods of carbon composite electrode materials, there is available a method of forming and depositing a carbon material through chemical vapor depositon any hydrocarbon or its derivatives on the surface of such a carbon material as graphite used as its core material. In this instance, the deposited carbon material shows a turbulent layer structure. The system needs to be held at about 1000.degree. C. for a long period of time so to deposit the carbon material having such a turbulent layer structure. Under such conditions, this method is not practically useful, because a large amount of a tarry product is generated by side reactions.